Many types of tools, including many types of hand tools, incorporate cutting edges for cutting various types of workpieces. For example, hand tools having a pliers-type of construction may include cutting edges. Pliers-type hand tools generally include a pair of elongated integral members (or pliers “halves”) each having a handle portion at one end and a jaw portion at an opposite end. The elongated members are pivotally connected to one another such that when the handle portions are opened and closed, the jaws open and close. Each jaw may be shaped to include an integral cutting edge along all of its length (e.g., a pair of dedicated wire cutters) or along a portion of its length (e.g., a pair of pliers that include cutting edges).
Conventional pliers that include cutting edges are difficult and expensive to manufacture. Each pliers half is an integral metal structure that is initially formed in a metal forging operation. After forging, each pliers half is machined to further shape and define various pliers features, including roughly machining in an integral cutting edge in each pliers half. Enough metallic material is left in the cutting edge area of each jaw to allow further shaping of the integral cutting edge. The two pliers halves are then movably connected to one another by, for example, pivotally connecting the halves to one another with a center rivet.
When machining the cutting edge in each pliers half, the machining process generates a recess or pocket on the back side of the cutting blade. FIG. 27 illustrates a known pliers half having a recess or pocket 240 on the back side of the cutting blade 250. When using these known pliers, the scrap material of the item being cut often gets caught in this recess or pocket 240 which requires the user to turn the pliers over so that the scrap material can fall out or be shaken out. If this scrap material is not removed from the recess or pocket 240, this scrap material can have an adverse affect on the next cutting operation. One aspect of the present invention is to provide pliers that prevent the possibility of scrap material adversely affecting subsequent cutting operations.
The metal of the pliers is then treated by, for example, heat treating the metal, to increase the metal hardness. Metal hardness may be increased from 35 Rockwell C Hardness (or “HRC”) to 50 HRC, for example, to make the metal strong enough to withstand everyday use. The amount of hardness increase depends on several factors including, the type of pliers being constructed and the types of jobs for which the pliers will be used. During heat treatment, the metal of the pliers moves and may become distorted.
The movement and/or distortion of the metal may be especially pronounced in hand tools that are long and thin and that have intricately machined features, such as pliers. Consequently, after heat treatment, the pliers are shaped and/or straightened to, for example, assure that the handle portions and jaw portions are properly shaped and properly aligned with one another. During this shaping process, the cutting edges are brought back into rough alignment with one another. This shaping and straightening is done manually by skilled labor and is therefore time consuming and expensive.
The cutting edges are then further shaped and aligned with one another by filing off some of the excess material in the cutting edge area of each jaw portion. This operation is often done manually by a skilled worker using a hand file or a fine grinding wheel. The two halves must be carefully shaped so that the cutting edges meet perfectly when the jaws of the pliers are in their closed position. If too much material is removed, the pliers are ruined. Each cutting edge must be filed/ground to have a sharp edge and so that when jaws are closed, the cutting edges are immediately adjacent one another or abut one another. When the cutting edges are shaped manually, the exact shape and quality of each cutting edge varies from one pair of pliers to the next. Manually-shaped cutting edges are also limited to having a simple bevel (when viewed in cross-section or “profile”). This edge configuration is not the best for all cutting applications. Most of the labor cost involved in the manufacture of pliers is incurred during the manual shaping operation in which the cutting edge of each pliers jaw is shaped.
After the cutting edges are filed/ground, the cutting edges are heat treated to increase the hardness of the cutting edges. The cutting edges may, for example, be treated to have a hardness of between 55 HRC and 65 HRC. These hardness values are outlined in the standards established by the American Society of Mechanical Engineers (ASME). The entire body of the pliers should not be hardened to this degree, however, because that would make the body of the pliers too brittle. Often the cutting edges are hardened using an induction heat treatment operation. During this operation, the cutting edges and a portion of the metallic material surrounding the cutting edges are heated rapidly using a localized heat source. When the cutting edges reach the desired temperature, they are quenched which increases the hardness of the cutting edges. This heat treating operation can be imprecise, however, and may result in each cutting edge having a variable hardness along its length or may harden the metallic material surrounding the cutting edges to a degree which renders the pliers prone to cracking, particularly if the metallic material of a pliers body is excessively hardened in the area of the pivot joint because the pivot joint area is highly stressed during operation of the pliers. After the blades are quenched during hardening, they are then tempered for toughness.
It can be appreciated that cutting edges formed in pliers made using conventional methods require extensive hand labor, are of inconsistent quality and are otherwise inherently limited. In general, pliers with good quality cutting edges are difficult, time consuming and expensive to produce using conventional methods. The mark of good quality cutting pliers is the ability of the pliers to cut bond paper cleanly when the paper is positioned anywhere along the cutting edges of the hand tool. This test is specified in ASME specifications and in other world standards for hand tools. This test indicates how accurately the cutting edges meet when the jaws are in their closed position. Perfectly matched cutting edges are important for cutting soft wire such as copper and for cutting fine strands of wire such as those found in lamp cords. The cutting edges of pliers formed by conventional methods are also limited due to cost to having a simple bevel shape. This shape is not necessarily the best cutting edge shape for a particular material or application.
Another test that indicates how accurately the cutting edges meet when the jaws are in their closed position is a light test. Specifically, light passing through the closed pliers cutting edges is viewed as a defect detrimental to cutting performance. That is, even the slightest deviation from straight in the cutting edges manifests itself as visible light when the jaws are closed and held up to the light. For example, FIGS. 22 and 23 illustrate pliers having a single cutting blade 260 that works cooperatively with an anvil 270 on an opposing jaw. The cutting edges of the blade 260 and anvil 270 are not perfectly straight due to typical manufacturing deviations, which allows light to pass between the edge of the blade 260 and the anvil 270. One aspect of the present invention is to provide pliers that reduces the possibility of light passing through cutting edges of pliers when they are closed together.
Generally, each cutting edge must be sharp and must be formed of a material that is hard enough to resist either plastic or permanent deformation under stress and to resist wear by abrasion. If, for example, the cutting edges become permanently deformed during a cutting operation, this deformation makes the cutting edges permanently dull which impairs cutting ability. Therefore, a hard material should be used to construct the cutting edges. The entire body of conventional pliers is made of a single material, however. A cutting edge made of a hard metallic material such as a highly alloyed steel, for example, will cut well, but a hand tool constructed entirely of a highly alloyed steel is expensive and is not commercially feasible. In addition, it may not be possible or desirable to make an entire hand tool such as a pair of pliers with a material that is optimized for forming a cutting edge because of the processing limits of the material. Therefore, manufacturers of pliers and other hand tools that include integral cutting edges must often compromise between selecting the best material for a cutting edge and selecting a cost effective material.
There is always a need in the tool making industries to improve tool quality and to lower production costs.